FIG. 1 illustrates a prior art system 10 for converting variable frequency multiple phase alternating current into multiple phase current of constant frequency. The system 10 has three inputs 12, 14 and 16 which are respectively from phases A, B and C of a variable frequency source of alternating current such as a three phase alternator driven by a power take-off without speed regulation from a propulsive engine in an airframe. A three phase transformer having primary windings 20, 22 and 24 and secondary windings 26, 28 and 30 is utilized to process the multiple phase current as follows. A first terminal of the secondary windings 28, 30 and 32 is coupled to the neutral N and the second terminal of the windings respectively provides a phase output with each of the phase outputs from the secondary windings respectively being phase displaced by 120.degree.. A full-wave rectifier 32 functions to apply pulsating current to the positive input 34 and the negative input 36 of a conventional three phase inverter with neutral and three phase load 38. The three phase load may be an unbalanced load on which current on the neutral N flows. A first group of diodes 40 consisting of diodes 42, 44 and 46 poled in a first direction applies pulsating positive current to the positive input 34 which has a frequency 3f with respect to neutral 62 where f is the fundamental frequency of the three phases of current inputted on the three phases 12, 14 and 16. Similarly, a second group of diodes 48, poled in the opposite direction to the diodes 40, consisting of diodes 50, 52 and 54 applies negative pulsating current to the input 36 at a frequency 3f with respect to the neutral as described above. A series circuit 56 consisting of capacitors 58 and 60 connects the positive input 34 to the negative input 36. Junction 62 is coupled to the neutral N.
The capacitors 58 and 60 function as filter capacitors to shunt the ripple frequency 3f to the neutral to prevent the application of substantial current at the ripple frequency to the three phase inverter with neutral and three phase load 38 which would cause the generation of undesired harmonics. In order to insure that the undesired ripple current at frequency 3f is shunted to the neutral, a relatively large capacitance must be used. This relatively large capacitance represents a weight penalty which could be minimized if the undesired ripple frequency of a higher frequency was present. Accordingly, the utilization of the prior art system for converting variable frequency multiple phase current into multiple phase current of constant frequency as illustrated in FIG. 1 is disadvantageous in airframes as a consequence of the weight penalty involved with the capacitances 58 and 60.